I think my hunch was correct. I think a reporter read a WHO document and misinterpreted what it says. I couldn't really find any more articles mentioning that possibility, which is a tip off. This other article pointed me to the apparent source of the flu + HIV mutating idea. Then I went and found the original WHO document here .

There's one sentence in the short document that apparently led to this surprising news report:

"Although there are inadequate data to predict the impact of a possible human influenza pandemic on HIV-affected populations, interactions between HIV/AIDS and A(H1N1) influenza could be significant."

However, "interaction" in this context is not referring to flu and HIV mixing genetically, creating some new super virus. It is simply referring (if you read the whole document, it's quite clear) to the possible additional complications of HIV-infected people also getting infected with the H1N1 flu and being more susceptible because of their weakened immune systems.

Anyway, that's my take on it.